1. Field of the Invention
The present invention is generally related to cellulose esters, and more particularly to cellulose based optical film materials.
2. Description of the Prior Art
Cellulose triacetate and derivatives exhibit less double refraction. Due to their moderate double refraction, cellulose triacetate derivatives have frequently been employed for production of protective optical films used for the polarizing plate of liquid crystal displays. Commonly, the polarizing plate has such a structure that a polarizing film comprised of a polyvinyl alcohol film and the like, in which iodine or dyes are absorbed and oriented, is laminated on both sides with transparent resin layers. Frequently employed as these transparent resin layers are protective films that are comprised of cellulose triacetate derivative films.
In recent years, development of liquid crystal displays to achieve a large-sized image screen of a high image quality has increasingly been made to produce advanced and compact monitors in lieu of the conventional nonportable CRT-based TVs. In conjunction with this, requirements for an advanced protective film for the polarizing plate in a liquid crystal display have become more stringent. Therefore, new cellulose based optical film materials of higher Tg and more handy forming method are still in large demands in terms of both economic effect and utilization in display industry.